More power!

I am a newbie to LS1 OBDII land, but I come from GN and Mustang experience. Those cars could adjust to changes, why can't LS1s? The LS1 ECM has the same inputs as the older systems, so why does it need a "tune" to run right? MAF, O2, TPS, fuel pressure, timing, knock detection -- the same inputs, why can't LS1s deal with improved breathing like the old Ford 5.0 liters and the Buick GNs? I need educated.

Thanks,

Fred

horist

To start, the PCM (especially in F-Bodies) is detuned from the factory... the LS1 can run more timing that it's setup for stock..

Once you get a cam it's a necessity to raise the rev limiter/change shift points

Once airflow characteristics change the MAF becomes "un-calibrated" kinda... (Probably the same as 5.0 stangs and GNs? only now w/the enhanced logging capabilities easier to see?)

at WOT a static table is used for power enrichment... assuming your LTRIMs are locking to zero , this static table can cause you to run rich or lean at WOT ... so there's some adjustment there to get more power

Torque Management (especially in 01 and 02 cars) kills the car between shifts...

There are more but that's a start...

More power!

Thanks for the start, Horist. Here are some follow up questions:

Detuned PCM? I was under the impression that fending off knock retard in the LS1 was always a problem. Have to run 93 octane fuel and such. From what I have seen, adding a degree or three to timing doesn't make that much difference in power levels.

On cams -- from running my Performance Trends Engine Analyzer software, it appears that most of the common reasonable (emissions compliant or near) LS1 cam grinds are done making power before 6200 rpm. Isn't the stock LS1 rev limiter 6200 rpm? I have experience with a few Prostreet cars that had big cams (260+ duration at 0.050) and they had power peaks below 6500 rpm. Some overrev is nice, but can't a "plug in box" like from Hypertech and such push the limit up?

The MAF should detect the increased air flow and change the injector pulse rate accordingly to maintain A/F ratio. At WOT, the static table may have fuel values that are too low -- the old Buick GN ECM just had the injectors go to 100% I believe and you could adjust the fuel pressure to dial in the A/F. If the static values are too low (being programmed for 300hp and not 350hp), then why do so many LS1 cars run rich when the breathing is improved?

Torque mgt sounds like a transmission saver. I have 6-spd, so I suppose it does not affect manual trans cars?

Thanks,

Fred

Turo

iTrader: (23)

Knock retard isn't a general problem to all LS1's. A lot of times its false knock (exhaust banging, etc...). The 93 fuel is a requirement I imagine because these motors have fairly high compression from the factory. About the cams, true that a lot of the emissions-friendly cams are done making power below 6200 rpm's, but lately there has been a big increase in 'standard' LS1 cam sizes. For instance, my cam peaks at around 6400ish, I shift it at around 6700. A hypertech can move the rev limiter, but it gives you very limited control (no air/fuel, airflow, or idle tuning capability). The maf does detect the increased airflow, but its not perfect, and tuning helps squeeze much more power out of it by adjusting the air fuel mixture (not to mention helps with drivability once you have a big cam). By the way, torque management is non-existant in 6-speeds (i believe).

Predator

Some of the mods that are done go beyond the range that the PCM can adjust to. For example, if you did headers, intake, cat delete, free-flowing exhaust, that would push your LTFTs beyond the PCM's range, throwing lean codes.

If you upgraded your injectors, for example, you'd need to recalibrate the injector flow rate table, etc. Also, as Mike mentioned, the factory tune on f-bodies is way rich, you'd want to adjust that too, even on a completely stock car. Not to mention all the other stuff like when the fans go on, torque management, and so forth.

slow

iTrader: (7)

88-93 5.0's use a RPM vs Spark for WOT timing, so the airflow does not play such a critical part in the timing curve like the ls1's. The 5.0's also use the maf for everything, and it is not really compared to a ve table like the ls1 cars seem do.

Ryan

More power!

OK, so some of the reasons to "tune" the stock programming when making changes from the stock hardware are:

-- the LS1 PCM has a limited range of capability with the factory programming and likes to run rich
-- if the LTFTs (long term fuel trims) go out of some factory-programmed normal range, then the ECM throws lean codes (even if the A/F ratio is reasonable because the factory programming is really rich apparently)
-- unlike older PCM controls that rely heavily on the MAF input, the LS1 has a VE table (volumetric efficiency?) that it compares the MAF input to and if it doesn't jive within the orginal factory limits then the car can run poorly or throw codes.

Did GM put some "fuzzy logic" into the programming to try to out-think the sensor inputs? I seem to remember from my GN days that the newer MAF for LT1/LS1 cars was a good upgrade for the Buick since the old Buick MAF maxed its signal at 300hp or so. The LT1/LS1 was supposed to almost double the signal range. Guess that doesn't matter to the LS1 PCM since some flaky overlapping programming "buggers up" the outputs if the inputs are not in a stock range.

Thanks for all the replies!

92SilverSHO

iTrader: (3)

yeah one thing i would recommend is 93 octane, AS soon as i started putting 91 in the car, blew a cat, i get KR down low and up high and my ltrims are very positive, just from gas, either way its costing me, damn montreal gas!!! my car loved the true sunoco 93 it had for over a year.

foff667

iTrader: (2)

ls1's from the factory are tuned to go to like 11.7:1 a/f at wot for one, not nearly ideal for the most power. Gear changes arent just replacing a speedo gear anylonger as its in the program. Cams rarely idle well with stock tuning unless its something small and on a 114+lsa...most people like a little lope my 231/237 would barely idle on its own with no tuning...I just got done doing some tuning on a 230/236 cam last night that again even with the idle speed bumped to 1000 it wouldnt start and hold and idle for its life there are other things in the programming that need to be changed for it to start & hold and idle on its own. As far as mustangs being able to adjust for parts better tell that to the pre 90' mustangs that had SD. As far as rev limiters and shift points go if your cam peaks at 6200-6300 where do you intend to shift? I shifted at 6800 and I dont believe theres any handheld that can get your shifts done accurately. If you search a little bit you can probably find someone in your area that will do a good tune for you cheap since the price of licensing has come down so much over the past year. Why would you even try and compare a prostreet application with what hypertech can do? My cam peaked at 6300rpms and alot of the larger cams peak at 6500+ do you think hypertech can bump the rev limiter to 6800-7000 rpms where alot of these guys need to spin to to get the best et/mph out of their car?

2MuchRiceMakesMeSick

TM does exist on 6spds. Just not as complex. It still pulls timing from the engine.

Mainly you want to tune to get the most out of your engine and in some cases (like my old car) so you can drive it. The boundaries are not set high enough for the pcm to learn something that radical.

Cal

iTrader: (1)

There is no way a computer can measure your engine's volumetric effeciency; that data has to be entered into a table. And if you change from the stock cam to a larger one, the VE will change dramatically. For my TSP235/240 cam, I had to adjust all points below 2000 rpm to get it to run right.

slow

iTrader: (7)

Do you mind sharing how VE is calculated then?

Ryan.

foff667

iTrader: (2)

https://ls1tech.com/forums/pcm-diagnostics-tuning/149741-ve-table-cracked.html

zo6vetteman2003

iTrader: (1)

I had the same problem with my ZO6 after the new cam install. It ran good the first day on some tuning, but when it started to learn the new tune, I encontered the idle and starting problem. I also had a slight leak on my aftermarket intake system, so before I would need to drill the throttlebody blade, I fixed the leak and kept the drilling as a last resort until I knew what the problem was. What I ended up doing was slightly advancing it alittle at a time when the engine was up to operating temperature, that it would start right away and not stall, because I knew my fuel injectors were also undersized. The time it takes for relearn is also a factor. So, what I ended up doing was getting it to where it would idle at 800rpm and drove it for well over 100 miles for relearn, until my new properly sized injectors arrived. I installed the injectors and retuned the spark advance and now it runs great no problems. Trial and error is what I had to do at first until the proper parts to support the new found power arrived. I don't know what mods. that LS1 has before the cam install, but the cam size and idle speed is agressive. I would take a look at getting the air in for idle without having to change your throttle position, and make sure you are getting enough fuel to support it.

foff667

iTrader: (2)

i knew what needed to be done...but since i no longer have my fbody to toy/experiment with i wanted to see if it would at all idle with only idle adjustments...i threw in the #'s i knew would work and got it to idle/startup just fine. The person had some valvetrain issues to get fixed so next week I'll finish it up...I try to keep changes to a minimum but when you go to larger and larger cams there just more stuff that needs to be changed that was my point.